1. Field of the Invention
The invention relates to a fuel cell system and a method for operating the same.
2. Description of the Related Art
In fuel cell systems where hydrogen gas is used as fuel, the anode exhaust of the fuel cell stack may be recycled back to the fuel cell's anode to make use of the surplus hydrogen in the exhaust. To prevent accumulation of impurities contained in the hydrogen gas inside the anode compartments of the fuel cell stack, however, the hydrogen has to be purged from time to time. In DE 199 44 541 A1 such a fuel cell system is disclosed. In addition to problems arising due to the interruption of the fuel cell operation, purging of hydrogen to the ambient environment may not be acceptable, as discharging of raw fuel may be a problem to the environment. The inclusion of a purifying unit in the recycling loop to avoid purging has been suggested, however while reactive impurities might be removed by appropriate catalytic reactions, inert impurities cannot be easily removed. If, as disclosed in another embodiment of DE 199 44 541 A1, the purged hydrogen is burned in a catalytic burner, the catalytic component is highly stressed by the frequent high load of hydrogen pulses.
Accordingly, there remains a need for a fuel cell system where impurities can be removed from the same without purging.